This morning, when Rev. Edward Sarrazin learned of the black graffiti defacing the exterior of the Mission San Xavier del Bac, his emotions fluctuated between sadness and anger.

"When I saw it, my heart dropped," he said. "I was also outraged that they would desecrate such a historic landmark."

The vandalism, discovered early this morning, is under investigation by the Tohono O'odham Nation Police Department. 

Workers were busy this morning removing graffiti from the walls of the mission, south of Tucson in the San Xavier District of the Tohono O'odham Nation.

While the interior of the church was unaffected, vandals damaged the mission's white, lime-mortar walls; the courtyard walls; a sidewalk; and a nearby tribal cemetery. 

By early morning, work crews had already removed the most obvious markings from the mission's front walls, which will have to be replastered.

During today's 8:30 a.m. mass, Rev. Sarrazin said he "prayed for the person who did this, that their heart would be softened."

"The church has withstood earthquakes and lightning strikes," he said. "We'll get over this."

Mission San Xavier del Bac was built between 1783 and 1797.

The mission is a National Historic Landmark and is known for its Spanish Colonial architecture in a Baroque style.

The mission is still an active parish and draws roughly 200,000 visitors each year.

In November, the mission was named to the 2016 World Monuments Watch — a list of cultural heritage sites that are fragile and in need of international attention in hopes of ensuring their future.

Since 1978, nonprofit Patronato San Xavier has overseen the preservation of and fundraising for the mission, also called the White Dove of the Desert.

"It was extensive case of sacrilege against an iconic, historic structure," said Chuck Albanese, president of the Patronato San Xavier board of directors.

"It's a sacrilege against the mission that represents all the values of this community, well beyond the church," he said.